X-ray system for taking short exposure x-ray photographs



Sept. 6, 1 938. c, "r, ULREY 2,129,383

X-RAY SYSTEM FOR TAKING SHORT EXPOSURE X-RAY PHOTOGRAPHS Original Filed July 25, 1955 nuns/w am?! by 4mm? I N 5 v '{NVENTOR 57 M! I BY ATTORNE Patented Sept. 6, 1938 UNITED STATES PATENT OFFICE X-RAY SYSTEM FOR POSURE X-RAY East Orange, N. J., assignor,

TAKING SHORT EX- PHOTOGRAPHS by mesne assignments, to Westinghouse Elec- Application July 25,

Renewed J a 9 Claims.

method and system X-ray photographs in a short in- My invention relates tothe for the taking of terval of time.

In systems of this the X-ray tube is usually taken from an energy users of the same. A usual method ray tube X-rays.

It is accordingly an object of my present in vention to provide a system for the taking of X- through the X-ray tube by causing substantially an instantaneous rise in the cathode heating temperature.

Another object of my present invention is the provision of from a condenser is; the tube is controlled by raising ng Company, East Pittsh Pa., a corporation of Pennsylvania 1933, Serial No. 682,063 nuary 22, 1936 of the cathode to the point of desired emissivity with an absence of appreciable time lag.

Another object of my present invention is the X-ray system wherein the X-ray tube excitation energy is taken directly from a Still further objects of my present invention will become obvious to those skilled reference to the accompanying drawing wherein means of a conductor l3 to one plate of the condenser 9 and the remaining plate of the condenser 9 is connected to the midpoint of the secondary winding 8 through a conductor M which is suitably grounded as at l5.

In a similar manner the remaining end of the secondary winding 8 is connected, by means of a conductor it, to the cathode of aseco-nd rectifying valve tube H. The anode of this latter valve is in turn connected to a second condenser device 13 through a conductor l9 and the remaining plate of this condenser i3 is likewise connected to the mid-point of the secondary winding 8 by means of the common conductor 14. The cathodes of the rectifying valves l2 and I1 receive heating current from a suitable source, such for example as low tension transformers 23 and 22, the primary windings of which may be connected to the commercial source of supply Ll, L2. Accordingly upon the cathodes of these valve tubes being heated to electron emissivity and the switch I closed, as hereinafter more fully explained, the condensers 9 and It will be charged during alternate half waves of the alternating current cycle with unidirectional high potential energy from the high tension transformer 5, as is Well understood in the art. It should also be understood that although I have shown, for the sake of simplicity, half wave rectification for accumulating a charge in a pair of condensers, full wave rectification might just as readily be employed and a single condenser of suitable capacity utilized.

The positive plate of condenser Sis connected by means of a conductor 23 to the anode terminal of an X-ray tube 24 and in a similar manner the negative plate of condenser is is connected, by means of a conductor 25, to the cathod'e of the X-ray tube 2 t, thus forming an output or discharge circuit for these condensers which discharge in series through the X-ray tube. The cathode of the X-ray tube receives heating current from a source of electrical energy which includes a low tension transformer 23 of relatively large current capacity in order that current in excess of that required for maximum emissivity of the cathode may be generated.

The primary winding of has one of its ends connected, conductor 21 and a suitable switch 28, to one of the supply conductors Ll, while its remaining end is connected by means of a conductor 29 through a fixed resistance element 30 and a variable resistance element 3! to the other supply conductor L2. A second resistance element, such as a tungsten filament lamp 32, the ohmic resistance of which rapidly with temperature changes, is adapted to be connected in electrical shunt relationship with the resistance element 30 by closure of a suitable switch arm 33. This switch arm 33 is connected, ating mechanism, such as a link bar and lever 3d constituting substantially a unitary double pole switch, with the switch arm I in the source of supply for the primary of the transformer 5 in order that upon opening of the switch arm 1 simultaneous closure of the switch arm 33 follows and vice versa.

Upon closure of the switch 28 the variable resistance 3! together with the resistance element 39 limits the current supplied by the source Ll, L2, to the primary winding of the transformer 26 which in turn maintains the cathode at a temperature where no appreciable electron emissivity occurs. Moreover, adjustment of the variable resistance 3i, while altering the maximum ohmic resistance included in the primary cir- .:cuit of the transformer 26, nevertheless mainsuitable actutains the current at a value which prevents any appreciable electron emissivity, as previously mentioned, and during excitation of the X-ray tube functions as a timing device as hereinafter more fully explained.

In the operation of my system is closed which heats the cathode of the X-ray paratively low temperature where no appreciable electron emissivity occurs. The switch mechanism 34, which prior to closure of the switch 28 is in a neutral position with both switch arms i and 33 open, is then moved to the left as shown in Fig. l to cause closure of the switch arm 1 and a further opening of switch arm 33. The high tension transformer 5 is accordingly energized from the source Ll, L2 and a high tension charge of unidirectional energy will be accumulated in the condensers 9 and I8 as before explained, over a period of time which is relatively long in comparison with the time of discharge thus prohibiting heavy surges upon the supply This charge may be regulated by lines Ll, L2.

means of a suitable auto-transformer (not shown) in the primary circuit of the transformer 5 and is also naturally dependent upon the capacity of the condensers 9 and 18. During the accumulation of this charge any leakage thereof, which would cause energization of the X-ray tube with attendant generation of X-rays, is prevented by the cathode being at a temperature insufllcient for appreciable electron emissivity.

Assuming now that the condensers 9 and I8 have been charged and it is desired to take a radiographic exposure the switch 34 is moved to the extreme right, as viewed from Fig. 1, which simultaneously opens the switch arm I and closes the switch arm. 33 thus connecting the resistance element 32 in shunt relationship with the resistance element 30.

The resistance element 32, having an initial low ohmic resistance due to its inherent characteristics because constructed of tungsten or similar metal, causes a momentary decrease in the ohmic resistance of the fixed resistance element 35!, which may also be a tungsten filament lamp similar to the resistance element 32 and having identical characteristics if desired, thus changing the total ohmic resistance in the primary circuit of transformer 26.

Upon this momentary decrease in the total ohmic resistance the heating current supplied to the cathode rises substantially instantaneously during this interval to a value in excess of that required for maximum emissivity of the cathode thus necessitating a heating transformer capable of generating current considerably higher than is usually employed.

This phenomenon may be better appreciated by reference to Fig. 2 wherein for the sake of simplicity the curves shown indicate current values when a direct current is applied to the cathode, and by assuming arbitrary values. It is to be understood, however, that these values may or may not be correct and that if the cathode is heated with alternating current, as shown in Fig. 1, the heating current wave will have a sinusoidal form and there will be a difference in the time interval during the change in cathode heating current from one value to another. Assuming, therefore, that with switch 28 closed and switch arm 33 open the resistance of element 3!] equals 100 ohms and that of resistance element 32, at room temperature, is 5 ohms, and the variable resistance element 3| is of such value, re-

tube 24 to a comgardless of its particular setting, that a maximum of only 3 ohms. This causes a momentary decrease in the total ohmic resistance in the primary circuit of the resistance of 100 after the lapse This results in a substantially instantaneous rise in cathode heating temperature with an attendant discharge of the energy accumulated in must be taken from In these prior art C of Fig. temperature rises in in the discharge -ray tube with the generation of X-rays of varying intensity.

On the other hand by the tation by a current of 6 amperes.

Moreover, by interrupting the source of supply to cause discharge of these condensers with attendant excitation of the X-ray What is claimed: 1. In an X-ray system for taking X-ray photopotential electrical energy, an X-ray tube pro- With a thermionic cathode and adapted to be energized by said means, means normally op-' erative to supply heating current to the cathode of said X-ray tube to maintain the same at a temperature insufiicient for electron emission to prevent said first mentioned means from energizing said X-ray tube, and means adapted to be connected to said last mentioned means to cause the same to momentarily supply a heating current to said cathode in excess of that required for maximum emissivity and then automatically decrease to a the purpose of raising the cathode heating temperature substantially instantaneously to the point of desired electron emissivity and to simultaneously cause energization of said X-ray tube by said first mentioned means.

2. In an X-ray system for taking X-ray photographs in a short interval of time, the combination of energy storage means, a source of rectified alternating current energy for accumulating a charge in said energy storage means, an X-ray tube provided 'with a thermionic cathode and connected to said energy storage means for energization by the charge accumulated therein, means normally operative to supply heating current to the cathode of said X-ray tube to main tain the same at atemperature insufficient for electron emission to prevent energization of said X-ray tube during the accumulation of the charge in said energy storage means, means adapted to be connected to said last mentioned means to cause the same to momentarily supply a heating current to said cathode in excess of that required for maximum emissivity and then automatically decrease the current to a constant value, for the purpose of causing a substantially instantaneous rise in the cathode heating temperature to the point of desired electron emissivity with an attendant simultaneous energization of said X-ray tube, and means operable to simultaneously render said last mentioned means operable and to interrupt the source of rectified alternating current in order to prevent the same from imposing a sinusoidal wave form upon the X-ray tube excitation energy.

3. In an X-ray system for taking X-ray photographs in a short interval of time the combination of an energy storage means adapted to accumulate a high potential charge of electrical energy, a source of rectified alternating current for charging said energy storage means, a discharge circuit for said energy storage means including an X-ray tube provided with a thermionic cathode, a source of heating current for the cathode of said X-ray tube including means normally operative to maintain said cathode at a temperature below that required for thermionic emission; and means adapted to be connected to said cathode heating source and operable to cause a momentary increase in the current supplied to said cathode in excess of that necessary for maximum emissivity, in order to cause a substantially instantaneous rise in the cathode heating temperature to the point of desired electron emissivity with attendant energization of said X-ray tube by the discharge of said energy storage means.

4. In an X-ray system for taking X-ray photographs in a short interval of time, the combination of energy storage means, a source of pulsating electrical energy for accumulating a charge in said energy storage means, an X-ray tube provided with a thermionic cathode and connected to said energy storage means for energination by the charge accumulated therein, a source of heating current for the cathode of said 75 X-ray tube including a resistance element northat required for maximum emissivity,

mally operative to cause the heating current to maintain the cathode at a temperature insufficient for electron emission to prevent energization of said X-ray tube during the accumulation of the charge in said energy storage means; and a resistance element adapted to be connected to said cathode heating source to cause a large momentary variation in the effect of said first mentioned resistance element and an increase in the current supplied to said cathode in excess of that required for maximum emissivity with an automatic decrease of current to a constant value after the lapse of a brief instant, for the purpose of causing a substantially instantaneous rise in cathode heating temperature to the point of desired electron emissivity with an attendant simultaneous energization of said X-ray tube.

5. In an X-ray system for taking X-ray photographs in a short interval of time the combination with an X-ray tube provided with a thermionic cathode and a source of high potential electrical energy for energizing said X-ray tube, of means for controlling the energization of said X-ray tube comprising a source of electrical energy for supplying heating current to the cathode of said tube, a resistance element included in said cathode heating source and normally operative to cause the same to supply a heating current to said cathode and maintain the latter at a temperature insuificient for electron emission; and a second resistance element adapted to be connected to said source having an initial low resistance which rapidly increases upon connection thereof to said cathode heating source, for the purpose of momentarily causing said cathode heating source to supply a current to said cathode in excess of that required for maximum emissivity, and both of said resistance elements reaching a state of equilibrium after the lapse of a brief instant to automatically reduce said current and maintain it at a constant value, in order to cause substantially an instantaneous rise in cathode heating temperature to the point of desired electron emissivity with an attendant energization of said X-ray tube by said high potential source.

6. In an X-ray system for taking X-ray photographs in a short interval of time the combination with an X-ray tube provided with a thermionic cathode and a source of high potential electrical energy for energizing said X-ray tube comprising an energy storage means adapted to accumulate a high potential charge from a source of rectified alternating current, of means for controlling the energization of said X-ray tube comprising a source of electrical energy for supplying heating current to the cathode of said tube, a resistance element included in said source and normally operable to cause the same to supply a heating current to said cathode and maintain the latter at a temperature insufiicient for electron emission; a second resistance element adapted to be connected to said cathode heating source having an initial low resistance which rapidly increases upon connection to said source, to momentarily cause said cathode heating source to supply a current to said cathode in excess of said second resistance element being adapted to reach a state oi equilibrium with said first mentioned resistance upon an increase in its resistance, to automatically reduce said cathode heating current and maintain it at a constant value, in order to cause substantially an instantaneous rise in cathode heating temperature to the point of 7. The method of taking short exposure X-ray photographs in a predetermined short interval of time with an X-ray tube having a thermionic perature, and the initial surge of current to be substantially at its maximum value.

8. The method of taking short exposure phoelectrical energy of a predetermined value, maintaining the cathode of the X-ray tube at a the accumulated charge.

9. The method of taking short exposure X- CLAYTON TRIDLE ULREY. 

